Most cinematographers start with a Bachelor's degree in Film and Cinema. After that they can usually land an apprenticeship or entry level job to get their foot in the door and start building a résumé. Once there are a significant amount of credits on their résumé, they've learned their craft, and their reel is impressive, they may be able to strike out on their own.
Eventually, anyone who is serious about the career will go back to school and receive a Master's Degree in Cinematography. After that, they can start applying for some of the bigger and better work. There aren’t many jobs to go around, so a DP needs to do everything they can to set themselves above the competition. Even if it means sitting in a very, very tall chair.